Compressed natural gas artificial gas lift

ABSTRACT

A gas lift capable oil well is artificially gas lifted by transferring compressed natural gas (CNG) from a compressed natural gas vessel of a mobile CNG storage system to a tubing-casing annulus of the gas lift capable well via a pathway. The CNG transfer occurs without the use of a compressor. A mobile unloader monitors and controls the flow of CNG from the vessel to the annulus.

CROSS REFERENCE

This application claims the benefit of priority from U.S. ProvisionalApplication No. 62/279,388, filed Jan. 15, 2016, titled “CompressedNatural Gas Artificial Gas Lift,” the entire contents of which arehereby incorporated by reference herein.

BACKGROUND

1. Field of the Invention

Various embodiments relate generally to the use of natural gas toartificially gas lift a gas lift capable or plunger-lift enabled oilwell, or a packerless completion gas well for dewatering.

2. Background

Oil and gas production wells collect oil and gas from naturalunderground reservoirs. When a pressure within such a reservoir isinsufficient to push oil (or other liquid) to the surface of a well(e.g., the wellhead) or the reservoir pressure provides an undesirablylow production flow rate, well operators can use a variety of artificiallift techniques to start or increase the upward flow of liquid (e.g.,oil) from the reservoir to the wellhead and production equipment. Onesuch artificial lift technique is called artificial gas lift.

In gas lift capable wells, gas (e.g., nitrogen or natural gas) is forceddownhole through a tubing-casing annulus disposed between a tubing and acasing of the well. The gas then enters the tubing (e.g., via gas liftvalves (or non-valved conduits) that connect the tubing andtubing-casing annuls), which decreases a density of liquid in the tubingand causes the liquid and gas to flow upwardly from the reservoir to thewellhead for production.

SUMMARY

One or more non-limiting embodiments provide a method for gas lifting agas lift capable well. The method includes transferring compressednatural gas from a compressed natural gas vessel of a mobile compressednatural gas storage system to a tubing-casing annulus of the gas liftcapable well via a first pathway, wherein said transferring occurswithout the use of a compressor. According to various non-limitingembodiments, avoiding the use of a compressor may provide a simpler,more cost effective gas lift operation.

According to one or more embodiments, during said transferring, apressure of compressed natural gas within the vessel is higher than apressure of compressed natural gas received by the tubing-casing annulusfrom the vessel.

According to one or more embodiments, a pressure of compressed naturalgas received by the tubing-casing annulus from the vessel during thetransferring is greater than 500 psig.

According to one or more embodiments, the method also includes:disposing an unloader in the first pathway, and using the unloader tocontrol a pressure of the compressed natural gas being provided to thetubing-casing annulus during the transferring.

According to one or more embodiments, the unloader comprises: ahigh-pressure outlet configured to provide compressed natural gas to thetubing-casing annulus without the use of a compressor, the high-pressureoutlet being disposed in the first pathway; and a low-pressure outletconfigured to provide compressed natural gas to a gas lift compressor ofthe gas-lift well.

According to one or more embodiments, the high-pressure outlet isconfigured to provide compressed natural gas at a pressure of over 500psig, and the low-pressure outlet is configured to provide compressednatural gas at a pressure of under 500 psig.

According to one or more embodiments, the method also includes using theunloader to control a flow rate of the compressed natural gas from thevessel to the tubing-casing annulus during the transferring.

According to one or more embodiments, the method also includes, duringthe transferring, actively controlling a flow rate of the compressednatural gas from the vessel to the tubing-casing annulus through thefirst pathway.

According to one or more embodiments, the method also includesmonitoring, via computer, operational conditions relating to thetransferring.

According to one or more embodiments, the method also includesautomatically controlling, via the computer, specific parameters of thetransferring based on information collected during the monitoring.

According to one or more embodiments, the transferring causes an upwardflow of downhole fluid within a tubing of the well.

According to one or more embodiments, the transferring increases anupward flow of downhole liquid within a tubing of the well.

According to one or more embodiments, the transferred compressed naturalgas flows down the tubing-casing annulus, enters a tubing of the gaslift capable well, and flows upwardly within the tubing.

According to one or more embodiments, the mobile compressed natural gasstorage system comprises a wheeled frame that supports the vessel.According to one or more embodiments, the method further includesdelivering the mobile compressed natural gas storage system to a site ofthe well before said transferring.

According to one or more embodiments, the method also includestransferring compressed natural gas from the vessel to the tubing-casingannulus by way of a compressor via a second fluid pathway.

According to one or more embodiments, the transferring via the secondfluid pathway occurs after the transferring via the first fluid pathway.

According to one or more embodiments, the compressor receives recyclenatural gas from production equipment of the well, compresses therecycle gas along with natural gas received from the vessel, and forcesboth recycle natural gas and natural gas received from the vessel intoand down the tubing-casing annulus.

One or more non-limiting embodiments provide a compressed natural gasartificial gas lift system comprising: a mobile compressed natural gasstorage system including a compressed natural gas vessel supported by awheeled frame, the compressed natural gas vessel containing compressednatural gas at a supply pressure; a gas lift capable well comprising atubing and a tubing-casing annulus; and a first fluid pathway thatconnects the vessel to the tubing-casing annulus, wherein there is not acompressor disposed in the fluid passageway, and wherein the system isconfigured to transfer compressed natural gas from the vessel to thetubing-casing annulus via the first fluid pathway.

One or more non-limiting embodiments provide a compressed natural gasartificial gas lift system comprising: a mobile compressed natural gasstorage system including a compressed natural gas vessel supported by awheeled frame; and an unloader configured to transfer compressed naturalgas from the vessel to a tubing-casing annulus of a gas lift capablewell via a first fluid pathway that does not include a compressor.According to various embodiments, the unloader comprises an adjustableflow rate regulator disposed in the first fluid pathway.

One or more of these and/or other aspects of various embodiments of thepresent invention, as well as the methods of operation and functions ofthe related elements of structure and the combination of parts andeconomies of manufacture, will become more apparent upon considerationof the following description and the appended claims with reference tothe accompanying drawings, all of which form a part of thisspecification, wherein like reference numerals designate correspondingparts in the various figures. In one embodiment, the structuralcomponents illustrated herein are drawn to scale. It is to be expresslyunderstood, however, that the drawings are for the purpose ofillustration and description only and are not intended as a definitionof the limits of the invention. In addition, it should be appreciatedthat structural features shown or described in any one embodiment hereincan be used in other embodiments as well. As used in the specificationand in the claims, the singular form of “a”, “an”, and “the” includeplural referents unless the context clearly dictates otherwise.

All closed-ended (e.g., between A and B) and open-ended (greater than C)ranges of values disclosed herein explicitly include all ranges thatfall within or nest within such ranges. For example, a disclosed rangeof 1-10 is understood as also disclosing, among other ranged, 2-10, 1-9,3-9, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of various embodiments as well as otherobjects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a diagrammatic side view of a high-pressure mode of acompressed natural gas artificial gas lift system according to variousembodiments;

FIG. 2 is a diagrammatic side view of a mobile compressed natural gas(CNG) unloader according to various embodiments of the systemillustrated in FIG. 1; and

FIGS. 3-4 are diagrammatic side views of optional low-pressure,high-pressure, and mixed low/high-pressure modes of CNG artificial gaslift systems according to various embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a CNG artificial gas lift system 10 according to oneor more embodiments. The system 10 includes a gas lift capable well 20,production equipment 150, a mobile CNG storage system 250, and a MobileCNG unloader 400.

Gas Lift Capable Well 20

As shown in FIG. 1, the gas lift capable well 20 includes a hollowcasing 30 that extends from a wellhead 35 of the well 20 at a groundsurface 40 down to an underground liquid reservoir 50 (e.g., containingnatural deposit of oil, water, and/or natural gas). The well 20 alsoincludes a tubing 60 that is disposed within the casing 30 and extendsdownhole from the wellhead 35. A tubing-casing annulus 70 (also called a“backside”) is formed between the tubing 60 and an interior wall of thecasing 30. Depending on the well configuration, a packer system 90 maybe disposed at the downhole end of the annulus 70 to seal the annulus 70from the production side, which may include both the inside of thetubing 60 and the entire casing interior below the packing 90.

According to various embodiments, the tubing 60 may comprise one or more(e.g., at least 1, at least 2, at least 3) parallel tubing strings, allof which are disposed inside the passageway in the casing 30. Accordingto various embodiments, packing 90 is used to seal the bottom of one,some, or all such tubing strings from the annulus 70. The bottom of oneor more other tubing strings can fluidly connected to the bottom of theannulus 70 (i.e., without packing). For example, the well may comprise adual gas lift configuration (e.g., two tubing strings disposed in asingle casing of a single well), as is known in the art. According tovarious embodiments, when multiple tubing strings are used, differentones of the tubing strings can extend to different depths.

The well 20 may comprise any type of gas lift capable well 20. In theillustrated embodiment, the tubing 60 includes a plurality ofvertically-spaced gas lift valves 80 that extend between the interior ofthe tubing 60 and the tubing-casing annulus 70. As is known in the art,the valves 80 are configured to selectively open so as to cause gas flowfrom the tubing-casing annulus 70 into the tubing 60 (e.g., based onpressures in the tubing-casing annulus 70).

According to various embodiments, the interior of the tubing 60 and thetubing-casing annulus 70 are additionally and/or alternatively fluidlyconnected to each other at the bottom 60 a of the tubing 60.

According to various alternative embodiments, the well 20 comprises aplunger-lift system or a U-tube configuration that omit packing orinclude unsealed packing.

Production Equipment 150

At the wellhead 35, the tubing 60 connects to production equipment 150via a conduit 160 to facilitate transfer of produced fluids (e.g., oil,water, and/or gas, etc.) from the well 20 to the production equipment150.

As is known in the art, such production equipment 150 may comprise aseparator 180 that separates liquids and gases. In the embodimentillustrated in FIG. 1, the separated gas flows through a conduit 190 tobe flared off or for further processing, collection, distribution,refining, etc. The separated liquid flows out through liquid conduit 200for further processing, collection, distribution, refining, etc.

CNG Mobile Storage System 250

As shown in FIG. 1, the CNG mobile storage system 250 comprises a CNGvessel 260 supported by a mobile frame 270. The vessel 260 may beremovably or permanently mounted to the mobile frame 270. In theillustrated embodiment, the mobile frame 270 comprises a wheeled frame270, in particular, a road-transportable trailer 270. However, accordingto alternative embodiments, the mobile frame 270 may comprise otherroad-transportable wheeled vehicles (e.g., truck). According toalternative embodiments, the mobile frame 270 may comprise arail-transportable vehicle (e.g., railroad car). According toalternative embodiments of the CNG mobile storage system 250, the mobileframe 270 may comprise a water-transportable mobile frame (e.g., abarge, boat, etc.). According to various alternative embodiments, themobile frame 270 may comprise a skid that is transportable via aflat-bed truck or trailer.

According to various embodiments, the vessel 260 may comprise one ormore CNG storage tanks. For example, as illustrated in FIG. 4, thevessel 260 comprises a plurality of CNG storage modules 280 that areloaded onto and removably (or permanently) supported by a 40 foottrailer 270 being pulled by a tractor 290. Each module 280 may comprisea plurality of CNG storage tanks.

According to various embodiments, the vessel 260 contains CNG at apressure that is (1) at least 500, 1000, 1200, 1500, 2000, 2500, 3000,3500, 4000, and/or 4500 psig (2) less than 5000, 4500, 4000, 3700, 3600,3000, 2500, 2000, and/or 1500 psig and/or (3) within any range withinsuch upper and lower values (e.g., between 500 and 5000 psig, between1000 and 3600 psig). According to various embodiment, CNG is transferredinto the vessel 260 at a location that is geographically separated fromthe wellhead 35 by at least 0.1, 0.5, 1, 2, 3, 4, 5, 7.5, 10, 15, 20,30, 40, 50, 75, 100, 150, 200, 250, 300, 400, and/or 500 miles. The CNGmobile storage system 250 is then transported (e.g., via road, rail,water) to the site of the well 20.

According to various embodiments, the CNG mobile storage system 250 maycomprise any of the mobile transport systems disclosed in WO2014/031999A2, the entirety of which is incorporated herein by reference.

According to various embodiments, the CNG mobile storage system 250complies with regulations for road transportation of CNG (e.g., DOT 49CFR, DOT SP 15136, ASME B31.3, and/or API RP 500/505).

According to various embodiments, the CNG mobile storage system 250 is40 feet long.

Mobile CNG Unloader 400

As shown in FIGS. 1 and 2, a CNG Unloader connects the vessel 260 to thewell 20 to control the flow of CNG from the vessel 260 to the well 20.

The unloader 400 comprises a mobile frame 410 and unloader equipment420. The mobile frame 410 may be similar to or identical to any of themobile frames 270 discussed above with respect to the CNG mobile storagesystem 250 (e.g., a trailer, skid, rail car, barge, boat etc.). Asillustrated in FIG. 4, the mobile frame 410 may comprise aroad-transportable, wheeled trailer that is 20 feet long or lessaccording to various embodiments. According to various embodiments, theCNG Unloader 400 complies with ASME B31.3 and/or API RP 500/505.

According to various embodiments, the unloader's mobile frame 410 iseliminated altogether, and the unloader equipment 420 is supported by(removably or permanently) the CNG mobile storage system's mobile frame270 so that the vessel 260 and unloader equipment 420 are transportabletogether as a unit to and from the well 20 site. User accommodations,discussed in greater detail below, may also be provided on the mobileframe 270.

As shown in FIG. 2, the unloader equipment 420 comprises an inletconduit 430 (e.g., a flexible hose, a series of rigid pipes, etc.) andinlet connector 440 configured to detachably connect the unloaderequipment 420 to the vessel 260 to receive CNG from the vessel 260. Theunloader equipment 420 comprises a high pressure outlet conduit 450(e.g., a flexible hose, a series of rigid pipes, etc.) and outletconnector 460 configured to connect the unloader equipment 420 to thetubing-casing annulus 70. As shown in FIG. 1, the connector 460releasably mates with a tubing-casing inlet connector/port 470 at thewellhead 35. According to various embodiments, the port 470 taps intothe blowoff preventer at the wellhead 35 and fluidly connects to thetubing-casing annulus 70. CNG flowing from the inlet conduit 430 to theoutlet conduit 450 passes sequentially through various components of theunloader equipment 420.

According to various embodiments, the unloader equipment 420 includes apressure regulator 480 that controls and reduces the pressure of CNGreceived from the vessel 260 so as to provide CNG to the tubing-casingannulus 70 at a pressure that is lower than a pressure within the vessel260. According to various embodiments, the pressure regulator 480 ismanually adjustable by a user so that the user can select the pressureat which CNG is provided to the tubing-casing annulus 70.

According to alternative embodiments, the pressure regulator 480 isautomated (e.g., via mechanical and/or electronic automation). Forexample, the pressure regulator may be computer controlled (e.g., viathe below-discussed computer 580).

According to various embodiments, the unloader equipment 420 includes aCNG meter 490 to meter the amount (e.g., in terms of mass and/or volume)of CNG that is transferred from the vessel 260 to the tubing-casingannulus 70. The meter 490 may comprise any suitable meter (e.g., anorifice plate meter).

According to various embodiments, the unloader equipment 420 includesflow rate control equipment 500 (e.g., a manual or automatic flow ratecontrol valve, a manual or automated choke valve, a manual or automaticadjustable orifice plate). According to various embodiments, the flowcontrol equipment 500 is manually adjustable by a user so that the usercan select the flow rate (e.g., in terms of mass and/or volumetric rate)at which CNG is provided from the vessel 260 to the tubing-casingannulus 70. According to alternative embodiments, the flow rate controlequipment 500 is automatically controlled (e.g., by the below-discussedcomputer 580).

The flow control equipment 500 may be configured to stop CNG flowentirely. However, additional shut-off valve(s) may also be positionedanywhere along the flow path between the vessel 260 and thetubing-casing annulus 70 (e.g., at the outlet port of the vessel 260, atthe inlet connector 470 of the wellhead, in or at the end(s) of theconduits 430, 450).

According to various embodiments, the unloader equipment 420 includes aheater 510. According to various embodiments, the heater 510 is poweredby natural gas that is supplied from the vessel 260. The heater 510 mayinclude a user-selectable temperature input, and may automatically heatthe CNG so as to deliver the CNG to the tubing-casing annulus 70 at adesired temperature or within a desired temperature range. The heater510 may be useful in situations where a large pressure drop from thehigh-pressure vessel 260 would otherwise cause excessive Joule-Thompsoncooling of the CNG. For example, the heater 510 may prevent cryogenicconditions along the flow path of the CNG.

Additionally and/or alternatively, the unloader equipment 420 maycomprise additional and/or alternative components 520, for example, anyof the unloader components described in WO2014/031999 A2, the entiretyof which is incorporated herein by reference.

According to various embodiments, the unloader equipment 420 includes amanually-actuatable distribution control valve 530 that can be manuallycontrolled by a user of the unloader 400 to selectively andalternatively deliver CNG to:

-   -   i) the high-pressure conduit 450 and connector 460 (e.g.,        providing outlet pressures above 500 psig),    -   ii) a low-pressure conduit 1070 and connector 1080, which is        discussed in greater detail below (e.g., providing outlet        pressures of under 200 psig), and/or    -   iii) a medium-pressure conduit 1075 and connector 1085, which is        discussed in greater detail below (e.g., providing outlet        pressures of 200-500 psig).

According to various embodiments, the valve 530 is a switching valve 530that enables only one of the conduits 450, 1070, 1075 and pressure modesto be used at any given time.

According to alternative embodiments, the valve 530 comprises aplurality of shut-off valves, one for each conduit 450, 1070, 1075 andpressure mode. The individual shut-off valves are connected toappropriate points within the CNG flow path(s) in the unloader 400.Separate pressure regulators 480, flow control equipment 500, and otherunloader equipment 420 may be provided for each of the low, medium,and/or high pressure conduits 450, 1070, 1075 and pressure modes so asto facilitate simultaneous transferring of CNG from the vessel 260 tothe well 20 via the unloader 400 at different pressures via parallelconduits 450, 1070, 1075 and connectors 460, 1080, 1085.

According to various embodiments, the unloader 400 may be configured tounload at only one of the pressure ranges (e.g., high, medium, low), inwhich case the valve 530 may be omitted, and all conduits may beconfigured for the designed outlet pressure range for the unloader.

According to various embodiments, the unloader equipment 420 includes avariety of pressure sensors 540 and temperature sensors 550 that measureCNG conditions at various points in the system 10 (e.g., the CNG beingreceived by the unloader 400, the CNG being delivered at the wellhead 35to the tubing-casing annulus 70). In FIG. 2, the sensors 540,550 areillustrated as being disposed at the connectors 440, 460. However, thesensors 540, 550 may alternatively be disposed at any other suitablepoint along the flow path of the CNG from the vessel 260 to thetubing-casing annulus 70.

As shown in FIG. 1, according to various embodiments, the unloader 400includes a check valve 560 in the conduit 450 (or otherwise disposedalong the flow path between the vessel 260, unloader 400, andtubing-casing annulus 70) to prevent backflow from the tubing-casingannulus 70 toward or into the unloader 400 and/or vessel 260.

According to various embodiments, the unloader equipment 420 includes acomputer 580 (e.g., a PC, laptop, tablet, programmable controller, orother computer) that is operatively connected to the sensors 540, 550,other equipment 420 (e.g., pressure regulator 480, CNG meter 490, flowcontrol equipment 500, heater 510), and/or other sensors in the system10 (e.g., flow rate and/or pressure sensors of the production equipment150; pressure sensors in the well 20 that measure uphole, downhole,and/or midhole pressures in the tubing 60 and/or the tubing-casingannulus 70; flow rate sensors in the well 20 that measure uphole,downhole, and/or midhole flow rates in the tubing 60 and/or thetubing-casing annulus 70) to track and record the operationalcharacteristics of the system 10 during gas lift operation. The computer580 may connect to a data transmission system (e.g., internet, WIFI,SCADA, LAN, WAN, Ethernet, digital or analog connection, phoneconnection, cellular network) to provide (1) a live feed of suchoperational characteristics of the gas lift system 10 and/or (2) providehistorical data for such operational characteristics for past operationof the gas lift system 10.

According to various embodiments, the computer 580 may calculate optimalpressure and flow rate using appropriate user inputs (tubing 60 size,casing 30 size, packer 90 depth, tubing 60 depth, etc.). Such userinputs may additionally or alternatively include well-type-specificinformation: (e.g., gas lift valves size and depth for gas lift wells20, information particular to a u-tube configuration well 20,information particular to a plunger lift well 20). According to variousembodiments, this reduces the setup and interaction needed by thecustomer and may improve production while the lift process is occurring.

While the individual components of unloader equipment 480, 490, 500,510, 520, 530 are illustrated in FIG. 2 in a particular sequentialorder, the components may alternatively be arranged in any other orderwithout deviating from the scope of the invention.

While a variety of exemplary unloader equipment 420 is illustrated, anycomponent(s) of the unloader 400 may be eliminated or altered withoutdeviating from the scope of the invention.

User Accommodations

According to various embodiments, user accommodations (e.g., a kitchen,bed, sleeping quarters, etc.) may also be provided on the mobile frame270 and/or 410. Such user accommodations may comprise any type ofaccommodations that are provided in an RV or long-haul tractor. The useraccommodations facilitate the user's extended well-site stay during theuse of the CNG mobile storage system 250 and unloader 400 to gas liftthe well 20. According to various embodiments, initially lifting thewell 20 may require anywhere from minutes to days of artificial gas lift(depending on the reservoir 50 pressure, depth, gas/liquid content orproportion, etc.), so the user accommodations facilitate the user'sextended well-site stay during the operation.

Operation of the System 10 in High-Pressure Mode

Hereinafter, operation of the system 10 in a high-pressure mode isdescribed with reference to FIG. 1. The CNG mobile storage system 250and unloader 400 may be used to (1) initially lift the well 20 (i.e.,start the flow of liquids from the reservoir 50 to the productionequipment 150 via the tubing 60), and/or (2) increase the rate ofproduction of liquids (e.g., oil) from the reservoir 50 to theproduction equipment 150 via the tubing 60 for ongoing artificial gaslift.

The CNG mobile storage system 250 and unloader 400 are delivered (e.g.,via tractor/truck) to the well 20 site. According to variousembodiments, the system 250 and unloader 400 are positioned so as to bewithin 600, 500, 400, 300, 200, 100, and/or 50 feet of the wellhead 35.According to various embodiments, the system 250 and/or unloader 400is/are positioned so as to be at least 25, 50, 75, 100, 150, 200, 250,300, 400, and/or 450 feet from the wellhead 35.

The user(s) connects the connector 440 to the vessel 260 and connectsthe connector 460 to the inlet connector 470 of the tubing-casingannulus 70. The valve 530 (if present) is set to provide CNG flow to thehigh-pressure conduit 450 and connector 460. According to variousembodiments, the user may be one person or multiple people. Variousactions (e.g., operating the unloader 400) may be carried out by a useraffiliated with the unloader 400. Various other actions (e.g.,connecting the unloader 400 to the well head 35) may be carried out bythe operator of the well 20.

The user then opens any shut-off valves and controls the unloaderequipment 420 so as to transfer CNG from the vessel 260 to thetubing-casing annulus 70 along a first pathway that includes: the vessel260, the connector 440, the conduit 430, the unloader equipment 420, thevalve 560, the conduit 450, the connector 460, and the inlet connector470.

As shown in FIG. 1, this transfer from the vessel 260 to thetubing-casing annulus 70 occurs without the use of a compressor or anyother driver that can forcibly move gas (e.g., a blower). According tovarious embodiments, the high-pressure mode of the system 10 (asillustrated in FIG. 1) is simpler, and/or less expensive than artificialgas lift systems that rely on a compressor to compress gas beforetransferring gas into the tubing-casing annulus.

The user monitors operational parameters of the system 10 and controlsthe operational parameters (e.g., flow rate, pressure, etc.) of theunloader 400 so as to cause the transferred CNG to gas lift liquid fromthe reservoir 50 to the production equipment 150 via the tubing 60. Theuser may vary the flow rate, pressure, etc. during the transfer (e.g.,varying the flow rate or pressure up and down). According to variousembodiments, the user manipulates the gas lift operational parameters tomaximize a production flow rate of liquids from the reservoir 50 to theproduction equipment 150.

According to various embodiments, as illustrated in FIG. 1, the usercauses the CNG mobile storage system 250 and CNG mobile unloader 400 todeliver CNG to the tubing-casing annulus 70 via the first pathway (ahigh pressure delivery pathway) at a delivery pressure (i.e., at theinlet into the tubing-casing annulus 70) that is (1) at least 300, 400,500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700,1800, 1900, 2000, 2250, 2500, 2750, 3000, 3500, 3600, 3750, 4000, and/or4500 psig, (2) less than 6000, 5000, 4500, 4000, 3700, 3600, 3000, 2500,2000, 1500, 1400, 1300, 1200, 1100, 1000, 900, 800, 700, and/or 600psig, and/or (3) in any range within such upper and lower values (e.g.,between 300 and 6000 psig, between 500 and 1500 psig). According tovarious embodiments, as illustrated in FIG. 1, during the transferringof CNG from the vessel 260 to the tubing-casing annulus 70, a pressureof CNG within the vessel 260 is higher than a pressure of CNG receivedby the tubing-casing annulus 70 from the vessel 260.

According to various embodiments, the transfer of CNG from the CNGmobile storage system 250 to the tubing-casing annulus 70 (1) starts anupward flow of downhole liquid within the tubing 60 to lift a well, (2)increases an upward production flow rate of downhole liquid within thetubing 60, (3) causes CNG received by the tubing-casing annulus duringthe transferring to flow down the tubing-casing annulus 70, enter thetubing 60, and flow upwardly within the tubing 60 to the productionequipment 150.

According to various embodiments, CNG from the CNG mobile storage system250 is used to initially lift the well 20. Once the well 20 begins toproduce naturally, artificial gas lift using CNG from the CNG mobilestorage system 250 is stopped.

Additionally and/or alternatively, CNG from the CNG mobile storagesystem 250 is used to provide continuous artificial lift to a producingwell 20 to increase the production flow rate of liquids from thereservoir 50 to the production equipment 150.

Compressor-Equipped Gas Lift System 1010

FIG. 3 illustrates a CNG artificial gas lift system 1010, which isgenerally similar or identical to the above-discussed system 10, exceptas discussed below. Accordingly, a redundant description of identical orsubstantially similar features is omitted. Unless otherwise stated, thesystem 1010 includes all of the features of the system 10.

As shown in FIG. 3, a gas recycle conduit 1030 replaces the flareconduit 190 of the system 10, and directs separated production gas to aninlet 1040 a of a compressor 1040. An outlet 1040 b of the compressorconnects via a conduit 1050 to the tubing-casing annulus 70. As aresult, gas that is produced by the well 20 and separated in theproduction equipment 150 is directed through the conduit 1030 to thecompressor 1040. The compressor 1040 compresses the gas and transfers itinto the tubing-casing annulus 70 via the conduit 1050 to facilitate gaslifting of additional liquids.

As shown in FIG. 3, a three-way joint 1060 (e.g., Y or T joint) isdisposed in the conduit 1030 upstream from the compressor 1040. As shownin FIG. 2, the unloader equipment 420 includes a low-pressure conduit1070 that leads from the valve 530 to a low-pressure connector 1080. Asshown in FIG. 3, the connector 1080 is connected to a mating connector1090 on one of the ends of the three-way joint 1060. As shown in FIG. 3,a check valve 560 is disposed in the conduit 1070.

According to various alternative embodiments, the check valve 560 in theconduit 450 and check valve 560 in the conduit 1070 may be combined intoa single check valve that connects at its upstream end to the unloader400 and branches out at its downstream end into the conduits 450, 1070with appropriate valves in each downstream branch. The system canalternate between low pressure delivery to the compressor 1040 and highpressure delivery to the wellhead 35.

As shown in FIG. 2, the unloader equipment 420 includes amedium-pressure conduit 1075 that leads from the valve 530 to amedium-pressure connector 1085. The medium-pressure connector 1085 canconnect to the connector 1090 on one of the ends of the three-way joint1060.

As shown in FIG. 3, a three-way joint 1100 may optionally be disposed inthe conduit 1050 downstream from the compressor (i.e., at an outlet sideof the compressor). A high-pressure connector 1110 that is similar oridentical to the connector 460 may connect to one of the ends of thethree-way joint 1100. As shown in FIG. 3, the high-pressure connector460 of the unloader 400 may be connected to the connector 1110.

As shown in FIG. 3, a surge conduit 1120 extends from the recycle gasconduit 1030 back to the vessel 260 of the CNG mobile storage system 250so that the CNG mobile storage system 250 can act as a buffer vessel toabsorb surge recycled gas flow in the conduit 1030. The conduit 1120connects to the vessel 260 via suitable valves and connectors (e.g., viaa branch connector off of the connector 400 (see FIG. 1).

As shown in FIG. 3, the surge conduit 1120 can also be used to collectexcess natural gas (e.g., recycled lift gas and/or natural gasoriginating from the reservoir 50) and store it in the vessel 260 forlater use (rather than flaring off such gas). For example, excessnatural gas produced by the well may be collected in the vessel 260 whenthe gas lift functionality of the system 1010 is not being used (e.g.,when sufficient flow exists without gas lift). Such excess natural gasflowing through the conduit 1120 to the vessel 260 can be dried.Additionally and/or alternatively, methanol may be injected into thenatural gas flowing into the vessel 260 via the conduit 1120 so as toprevent hydrates from forming inside the vessel 260. The excess naturalgas being collected in the vessel 260 can then be used to lift the welland/or power the system 1010 (e.g., the compressor 1040) as desired(e.g., when insufficient gas is flowing from the wellhead).

Operation of the System 1010 in Low-Pressure or Medium Pressure Mode

Hereinafter, operation of the system 1010 in low-pressure mode isdescribed with reference to FIG. 3.

If the well illustrated in FIG. 3 is not flowing, or if the productionflow provides insufficient recycle gas, then insufficient recycle gasmay be available to gas lift the well 20. In such circumstances, the CNGmobile storage system 250 and unloader 400 may be used to provide enoughsupplemental natural gas to initially lift the well 20 and/or increasethe rate of production of liquids from the reservoir 50.

The CNG mobile storage system 250 and unloader 400 are delivered (e.g.,via tractor/truck) to the well 20 site as described above with respectto the system 10.

The user connects the connector 440 to the vessel 260 (see FIG. 1) andconnects the connector 1080 to the connector 1090.

As shown in FIG. 3, the user then opens any shut-off valves and controlsthe unloader equipment 420 so as to transfer CNG from the vessel 260 tothe tubing-casing annulus 70 along a second pathway that includes: thevessel 260, the connector 440, the conduit 430, the unloader equipment420, the valve 530, the conduit 1070, the connector 1080, the connector1090, the three-way joint 1060, the compressor 1040, and the conduit1050.

The user controls the pressure 480 to provide low-pressure CNG to theinlet 1040 a of the compressor 1040. According to various embodiments,CNG is provided to the compressor 1040 from the vessel 260 at acompressor 1040 inlet 1040 a pressure of (1) less than 600, 500, 450,400, 350, 300, 250, 200, 150, 100, 75, and/or 50 psig, (2) more than 5,10, 25, 50, 75, 100, 150, 200, 250, 300 psig, and/or (2) within anyrange between any two such upper and lower values (e.g., between 5 and500 psig).

If the CNG pressure provided to the compressor 1040 is under 200 psig,the mode may be considered low-pressure according to variousembodiments. If the CNG pressure provided to the compressor 1040 isbetween 200 and 600 psig, the mode may be considered medium pressure.Different types of conduits, valving, connects, etc. may be useddepending on the pressure range for the CNG provided to the compressor1040. For example, low-pressure flexible hoses may be used forlow-pressure (e.g., 5-200 psig) delivery (e.g., via conduit 1070 andconnector 1080). Medium pressure equipment (e.g., conduit 1075,connector 1085) may be used for medium-pressure delivery. High pressureequipment (e.g., rigid pipes, valves, connectors, etc. configured toaccommodate high CNG pressure (e.g., pressure over 600 psig)) may beused for high-pressure delivery (e.g., via conduit 450 and connector460).

The compressor 1040 then compresses the CNG from the vessel 260 (as wellas recycle gas from the conduit 1030 if the well 20 is producing recyclegas) to gas lift pressures and delivers the compressed gas to thetubing-casing annulus 70 via the conduit 1050. The CNG mobile storagesystem 250 and unloader 400 thereby facilitate initial lifting and/orcontinuous artificial gas lift for compressor-equipped gas lift wellsthat have no recycle gas or recycle gas with insufficient pressureand/or flow rate.

Operation of the System 1010 in High-Pressure Mode

As shown in FIG. 3, the CNG mobile storage system 250 and unloader 400may alternatively be used in a high-pressure mode withcompressor-equipped wells. The CNG mobile storage system 250 andunloader 400 may operate in the same manner as described above inconnection with the system 10. In particular, the CNG mobile storagesystem 250 and unloader 400 bypasses the compressor 1040 and connectsthe unloader's high pressure conduit 450 and connector 460 to theconduit 1050 downstream from the compressor 1040 (or to a separatewellhead port like the connector 470 illustrated in FIG. 1). Accordingto various embodiments, this high-pressure, compressor-bypass route canbe used to surge high volume, high pressure CNG into the tubing-casingannulus 70 as flow rates that are higher than is possible via thecompressor 1040.

The user may switch between high-pressure direct (compressor bypass)delivery and low-pressure compressor-based delivery by actuating thevalve 530 as desired and appropriately modifying the pressure regulatorto provide appropriate pressure CNG (e.g., high pressure CNG for directinjection, low pressure CNG for injection into the compressor 1040).According to various embodiments, the user initially uses the CNG mobilestorage system 250 and unloader 400 in the high-pressure mode (i.e.,directly transferring high pressure CNG to the tubing-casing annulus 70via the first pathway without use of the compressor), for example toinitially lift the well and start production, and subsequently switchesto the low-pressure mode that transfers CNG to the tubing-casing 70 viathe second pathway and compressor 1040, and also relies on recycle gasfrom the flowing well. The low-pressure mode reduces the well system'sdependence on CNG from the CNG mobile storage system 250 by takingadvantage of gas produced by the well 20 (including gas that wasinitially provided by the CNG vessel 260 and already traversed thegas-lift path to the production equipment 150).

According to various embodiments, the CNG mobile storage system 250 andunloader 400 may be used temporarily to lift a well 20. Once liquidsstart to flow from the reservoir 50 to the production equipment 150 viathe tubing 60, the flow may be sustainable, such that further artificialgas lift can be stopped. If so, the CNG mobile storage system 250 andunloader 400 can be removed from the well 20 site after lifting for useat a different well 20 site.

Alternatively, the CNG mobile storage system 250 and unloader 400 may becontinuously used in a producing well 20 to provide extended (e.g.,continuous) artificial gas lift in order to increase a liquid (e.g.,oil) production rate of the well 20. Such extended (e.g., continuous)artificial gas lift is well suited for wells in which natural reservoirpressure is insufficient to provide natural lift and/or the natural liftresults in an undesirably low production rate.

According to various embodiments, the CNG mobile storage system 250 andunloader 400 may be kept at the well site for extended periods of time,even when not being actively used for artificial gas lift. The onsiteavailability of the CNG mobile storage system 250 and unloader 400,according to various embodiments, may provide (1) cost effective andresponsive unplanned lifting service, and/or (2) makeup gas when/if therecycle gas system fails (e.g., if the separator 180 slugs with fluid),thus starving the compressor 1040 of gas, regardless of gas productionrates from the well 20. The available onsite gas lift service providedby the CNG mobile storage system 250 and unloader 400 may keep thecompressor 1040 running and avoid trips on low suction pressure.

According to various embodiments, a single CNG mobile storage system 250provides enough CNG to initially lift the well 20. According toalternative embodiments, multiple CNG mobile storage systems 250 arerequired to provide sufficient gas to initially lift a well. Wheremultiple CNG mobile storage systems 250 are needed to initially lift awell 20 (or where continuous artificial lift is desirable using CNG froma CNG mobile storage system 250), a fresh CNG mobile storage system 250may be delivered to replace a depleted CNG mobile storage systems 250 asdesired. The unloader 400 may include multiple inlet connectors 440 sothat a fresh CNG mobile storage system 250 can be connected to theunloader 400 before a depleted CNG mobile storage system 250 isdisconnected. Appropriate check valves and other shut-off valving may beincluded to facilitate a continuous supply of CNG to the unloader 400during switch off between depleted and fresh CNG mobile storage systems250. The direct swap systems disclosed in WO2014/031999 A2 may be usedto facilitate swapping of the fresh and depleted CNG mobile storagesystems 250.

As used herein, “depleted” means depleted to an extent, and does notrequire complete evacuation of all CNG within a CNG mobile storagesystem 250. According to various embodiments, a CNG mobile storagesystem 250 may be considered depleted when the vessel 260 pressure fallsbelow a predetermined threshold (e.g., 2000, 1750, 1700, 1600, 1500,1400, 1300, 1200, 1100, 1000, 900, 800, 700, 600, 500, 400, 300, 200,100, 75, 50, 25 psig).

According to various embodiments, the passageways, fluid paths, andother conduits described herein may comprise any suitable conduit (e.g.,rigid or flexible piping, concrete enclosed passage, annular passagewaysbetween nested conduits). The various connectors may comprise anysuitable connectors for the temperature, flow rate, and/or pressuredesigned to flow through such connectors. The unloader 400 may include avariety of adaptors to accommodate connecting the unloader 400 to CNGsystems 250, vessels 260, and well 20 connectors of different types andmodels.

According to various embodiments, the use of the CNG mobile storagesystem 250 to artificially lift the well 20 may have variousnon-limiting benefits. According to one or more non-limitingembodiments, the use of CNG reduces or prevents detrimental oxygenintroduction into the well 20. Various nitrogen lifting procedures(e.g., the use of a filter to obtain nitrogen from ambient air) resultin significant oxygen being entrained with the nitrogen and causingexplosion possibilities and/or corrosion of metal downhole or productionequipment.

According to one or more non-limiting embodiments, the use of CNGreduces or avoids the step of purging nitrogen from the produced fluid(e.g., a mixture of gas and liquid) before commencing production, as isrequired for nitrogen-based gas lifting. Such purging frequently resultsin the waste of valuable hydrocarbons (e.g., natural gas) that areproduced from the well but are flared off as part of the nitrogen purgestep.

According to various embodiments, use of the CNG mobile storage system250 to gas lift a well 20 creates little or no disruption to theoperation of the well 20, and can be used to gas lift the well 20without interruption in well 20 production (if the well 20 is alreadyproducing prior to use of the CNG mobile storage system 250 forartificial gas lift).

The foregoing illustrated embodiments are provided to illustrate thestructural and functional principles of various embodiments and are notintended to be limiting. To the contrary, the principles of the presentinvention are intended to encompass any and all changes, alterationsand/or substitutions thereof (e.g., an alterations within the spirit andscope of the following claims).

What is claimed is:
 1. A method for gas lifting a gas lift capable well, the method comprising: transferring compressed natural gas from a compressed natural gas vessel of a mobile compressed natural gas storage system to a tubing-casing annulus of the gas lift capable well via a first pathway, wherein said transferring occurs without the use of a compressor.
 2. The method of claim 1, wherein, during said transferring, a pressure of compressed natural gas within the vessel is higher than a pressure of compressed natural gas received by the tubing-casing annulus from the vessel.
 3. The method of claim 2, wherein a pressure of compressed natural gas received by the tubing-casing annulus from the vessel during the transferring is greater than 500 psig.
 4. The method of claim 2, further comprising: disposing an unloader in the first pathway; and using the unloader to control a pressure of the compressed natural gas being provided to the tubing-casing annulus during the transferring.
 5. The method of claim 4, wherein the unloader comprises: a high-pressure outlet configured to provide compressed natural gas to the tubing-casing annulus without the use of a compressor, the high-pressure outlet being disposed in the first pathway, and a low-pressure outlet configured to provide compressed natural gas to a gas lift compressor of the gas-lift well.
 6. The method of claim 5, wherein the high-pressure outlet is configured to provide compressed natural gas at a pressure of over 500 psig, and the low-pressure outlet is configured to provide compressed natural gas at a pressure of under 500 psig.
 7. The method of claim 4, further comprising using the unloader to control a flow rate of the compressed natural gas from the vessel to the tubing-casing annulus during the transferring.
 8. The method of claim 1, further comprising, during the transferring, actively controlling a flow rate of the compressed natural gas from the vessel to the tubing-casing annulus through the first pathway.
 9. The method of claim 1, further comprising monitoring, via computer, operational conditions relating to the transferring.
 10. The method of claim 9, further comprising automatically controlling via the computer specific parameters of the transferring based on information collected during the monitoring.
 11. The method of claim 1, wherein the transferring causes an upward flow of downhole fluid within a tubing of the well.
 12. The method of claim 1, wherein the transferring increases an upward flow of downhole liquid within a tubing of the well.
 13. The method of claim 1, wherein the transferred compressed natural gas flows down the tubing-casing annulus, enters a tubing of the gas lift capable well, and flows upwardly within the tubing.
 14. The method of claim 1, wherein: the mobile compressed natural gas storage system comprises a wheeled frame that supports the vessel; and the method further comprises delivering the mobile compressed natural gas storage system to a site of the well before said transferring.
 15. The method of claim 1, further comprising: transferring compressed natural gas from the vessel to the tubing-casing annulus by way of a compressor via a second fluid pathway.
 16. The method of claim 15, wherein the transferring via the second fluid pathway occurs after the transferring via the first fluid pathway.
 17. The method of claim 15, wherein the compressor receives recycle natural gas from production equipment of the well, compresses the recycle gas along with natural gas received from the vessel, and forces both recycle natural gas and natural gas received from the vessel into and down the tubing-casing annulus.
 18. A compressed natural gas artificial gas lift system comprising: a mobile compressed natural gas storage system including a compressed natural gas vessel supported by a wheeled frame, the compressed natural gas vessel containing compressed natural gas at a supply pressure; a gas lift capable well comprising a tubing and a tubing-casing annulus; and a first fluid pathway that connects the vessel to the tubing-casing annulus, wherein there is not a compressor disposed in the fluid passageway, and wherein the system is configured to transfer compressed natural gas from the vessel to the tubing-casing annulus via the first fluid pathway.
 19. A compressed natural gas artificial gas lift system comprising: a mobile compressed natural gas storage system including a compressed natural gas vessel supported by a wheeled frame; and an unloader configured to transfer compressed natural gas from the vessel to a tubing-casing annulus of a gas lift capable well via a first fluid pathway that does not include a compressor, wherein the unloader comprises an adjustable flow rate regulator disposed in the first fluid pathway. 